Conventional utility networks supply utilities for commercial, residential and industrial purposes. In a typical electrical distribution system, for example, electrical energy is generated by an electrical supplier or utility company and distributed to consumers via a power distribution network. The power distribution network is often a network of electrical distribution wires (more commonly known as “electrical transmission lines”) which link the electrical supplier to its consumers. Additional devices, such as bus bars, switches (e.g., breakers or disconnectors), power transformers, and instrument transformers, which are typically arranged in switch yards and/or bays, are automated for controlling, protecting, measuring, and monitoring of substations.
Typically, electricity from a utility is fed from a primary station over a distribution cable to several local substations. At the local substations, the supply is transformed by distribution transformers from a relatively high voltage on the distributor cable to a lower voltage at which it is supplied to the end consumer. From the local substations, the power is provided to industrial users over a distributed power network that supplies power to various loads. Such loads may include, for example, various power machines, lighting, HVAC systems, etc.
Some electrical distribution networks, such as multi-phase alternating current (AC) networks, undergo heavier burden when large reactive loads are repeatedly connected to and disconnected from the distribution line. These variations in power circulation can result in low system efficiency and high energy losses. For instance, energy losses can occur when large inductive loads are connected to the distribution lines, which can produce an inordinate amount of lagging reactive current in the line.
In general, the power factor of an AC electric power system is the ratio of the real (or “active”) power used in a circuit to the apparent power used by the circuit. Real power, which is typically expressed in watts (W) or kilowatts (kW), is the capacity of the circuit for performing work in a particular time, whereas apparent power, which is typically expressed in volt-ampere (VA) or kilo volt-ampere (kVA), is the product of the current and voltage of the circuit. It is often desirable to increase the power factor of a system.
Power factor correction (PFC) can be achieved, for example, by switching in or out banks (or racks) of capacitors. A capacitor bank is typically composed of a number of discrete steps that can be switched in and out of operation. Each step is composed of a number of individual capacitors that are wired in parallel (or series, depending upon the system), and sum together to provide the total capacitance for the step. One conventional device used for controlling the switching of the capacitor banks onto and off of the distribution lines are power factor controllers. The controller device can switch the connectivity of the capacitor bank as needed to correct the power factor for the load detected at any given time. Conventional power factor controllers switch the capacitor bank into and out of the electrical line on the basis of a number of measurable parameters, such as reactive current, voltage, time, temperature, etc.
Power capacitors are naturally prone to aging effects that can change their electrical characteristics (e.g., capacitance, equivalent resistance, etc.), which in turn can reduce their effectiveness. Depending on the materials used, the design type, and the details of manufacturing, for example, some capacitors may be prone to different types of failure if their electrical characteristics change at a faster rate than expected from normal aging. In some cases, these failures can be mitigated by a self-protection mechanism, which is activated, for example, by overpressure, overtemperature, and/or overcurrent, removing the capacitor from the circuit. Other cases may lead to a failure where the self-protection mechanism fails to operate.
It is common today for capacitor bank installations to have very limited or no monitoring and diagnostics available, due in part to the expense associated with monitoring the health of individual steps within a capacitor bank. As a result of this limited monitoring and diagnostics, it is very difficult to detect operational problems before they occur in order to mitigate operational concerns and minimize service disruption through regular maintenance efforts.